Prior art lawn and garden vehicles and similar machines have employed hydrostatic transmissions. Such transmissions commonly include a control lever which is moveable from a neutral position to a forward position and wherein the degree of movement of the lever controls the speed of the vehicle employing the hydrostatic transmission. Movement of the lever from a neutral position to a reverse position causes the vehicle to be driven rearwardly, and the rearward speed of the vehicle is similarly dependent on the degree of movement of the control lever. One of the problems associated with the use of hydrostatic transmissions in lawn and garden vehicles and other similar vehicles, is that the operator's control mechanism may be ineffective to cause the transmission control lever to return to its precise neutral position. When the operator moves the drive control lever or foot pedal to a neutral position, the transmission control lever may be positioned such that the transmission is in a low speed forward or reverse operating condition.
With common hydrostatic transmissions the control lever may have a very narrow or small range of movement in the neutral operating position and such that only a minor change in the position of the transmission control lever may cause shifting of the transmission from neutral to forward or reverse. Additionally, the neutral position of the transmission control lever can vary from one hydrostatic transmission to another such that the control linkage of one vehicle may hold a transmission in the neutral position when the hand control lever or foot pedal is in a neutral position, while in another like vehicle, with the hand control lever or foot pedal in a neutral position, the control linkage may hold the transmission control lever in a position which for that particular transmission is either a forward or reverse driving position.
In prior art vehicles including hydrostatic transmissions, the apparatus provided for causing the transmission to return to the neutral position is commonly located in a position remote from the vehicle transmission and is also commonly relatively inaccessible. Such contructions prevent preadjustment of the neutral return device until substantial completion of the manufacture of the vehicle due to common dimensional variation of the many parts between the return to neutral mechanism and the transmission control shaft.
Another problem experienced with prior art return to neutral arrangements is that connecting linkages tend to wear as the vehicle is used and as the frame or other vehicle components deform with use, and the neutral return apparatus requires frequent adjustment. Such adjustment is commonly difficult because of inaccessibility of the adjusting mechanisms.